The presently known cryosurgical instruments are usually equipped with two heat exchangers, the first for cooling and the second for heating. The cooling heat exchanger is utilized for heat exchange between a cooling fluid and the operating end piece of the instrument. The heating heat exchanger is utilized for heating the cooling fluid leaving the instrument, whenever the enthalpy of the cooling fluid was not fully used for cooling the tissue adjacent to the operating end piece.
Cooling heat exchangers are known as having the simplest type of chamber construction, whenever the cooling fluid by-passes the cooled-down smooth walls thereof, or by-passes the cooled-down ribbed walls thereof, if these ribbed walls are present in the structure. Cooling heat exchangers may also be of the porous type of chamber construction, being formed usually from metallic grids or from perforated metallic foils, in such a manner that these metallic grids or foils have a good mutual thermal contact with each other.
The heat exchanger will also contain a heat detector and a heating element. The heat detector and the heating element are each so placed within the heat exchanger that each is immersed in the path of, and is washed by, the exit flow of the cooling fluid leaving the heat exchanger. The heating heat exchangers are usually formed by locating heating coils within a stream of the exiting gas leaving the heat exchanger.
The disadvantages of the above-mentioned chamber type of cooling heat exchanger consist of low efficiency caused by the small amount of heat transfer surface area. For example, in order for the chamber type of cooling heat exchanger to be able to achieve a transferring away from the body tissue being operated upon, of an amount of heat measured in units of watts, it becomes necessary for the heat exchanger to consume the cooling fluid at a rate measured in liters per minute.
Cooling heat exchangers equipped with the porous type of components have a higher order of efficiency. However the porous type does have the disadvantages of having its thermal efficiency suppressed due to thermal faults in the direction of flow of the cooling fluid and due to imperfect thermal contact with the outer jacket of the heat exchanger. A similar situation exists as well for the heating type of heat exchangers.
The above-noted disadvantages not only decrease the quality of the cryosurgery performed, but they also substantially increase the quantity of energy needed for utilizing the cryosurgical instrument. Because of the location of the heat detector within the exit flow stream of the cooling fluid leaving the heat exchanger, false information is obtained about the correct temperature at the surface of the cryosurgical instrument. This false information can result in complications during a cryosurgical operation; for example, not attaining the desired low temperature during cryolesis is one disadvantage. Another example of a complication is one which results from the situation wherein the thermometer shows a temperature reading above 0.degree. C., while the correct temperature at the surface of the end of the instrument touching the body tissue, is far below the freezing point. In this situation, there is injury to the tissue caused by the tearing away of tissue frozen together onto the operating end of the cryosurgical instrument.